A Case of Anaplasmosis Infection with Rash and Coinfection or Antibody Cross-Reactivity

Introduction: Tick-borne illnesses are on the rise in Maine and include Lyme disease, anaplasmosis, and babesiosis. Anaplasmosis is an infection caused by Anaplasma phagocytophilum, a bacterium of the Rickettsiales order. A. phagocytophilum is transmitted by Ixodes scapularis, also known as the blacklegged or deer tick. Symptoms of fever, chills, headache, malaise, cough, and confusion usually occur within several days of the tick bite. Rash in patients with anaplasmosis is uncommon and may indicate coinfection with another tick-borne disease. Laboratory values may show thrombocytopenia, leukopenia, and transaminitis. Bacteria may be visible within the granulocytes on peripheral smear. Rocky Mountain spotted fever is another tick-borne illness, transmitted by American dog ticks in the eastern United States. American dog ticks in Maine are not known to transmit the bacteria that causes Rocky Mountain spotted fever. Clinical Findings: A 74-year-old man was admitted with fever, acute encephalopathy, acute kidney injury, transaminitis, and petechial rash 2 weeks after a tick bite. Clinical Course: The patient was started on doxycycline for presumed tick-borne illness. Laboratory results for antibody screening were negative for Lyme, Anaplasma, Babesia, and Ehrlichia. However, testing with polymerase chain reaction returned positive for A. phagocytophilum on hospital day 4. The petechial rash worsened on hospital day 5, and laboratory results for spotted fever group antibodies showed a 4-fold increase in serum immunoglobulin G levels over 4 weeks. He was discharged in stable condition. Conclusions: This patient represents a case of anaplasmosis with (1) rash and antibody cross-reactivity between A. phagocytophilum and spotted fever group antibodies or (2) a less likely co-infection with Rocky Mountain spotted fever or other spotted fever or Rickettsia bacteria.